The present invention generally relates to technology for alleviating a hidden node problem and, more particularly, to a method for alleviating a hidden node problem by setting a restricted access window in a wireless local area network (WLAN) system.
With the development of information and communication, various wireless communication technologies have been developed. Among technologies, wireless local area network, (WLAN) denotes technology for allowing wireless access to the Internet in homes, businesses or specific service areas using a mobile terminal such as a personal digital assistant (PDA), a laptop computer, a portable multimedia player (PMP), a smart phone, or a tablet PC, based on radio frequency (RF) technology.
Standards for WLAN technology have been developed as Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards. IEEE 802.11a provides a data rate of 54 Mbps in a 5 GHz unlicensed band. IEEE 802.11b provides a data rate of 11 Mbps using a direct sequence spread spectrum (DSSS) in a 2.4 GHz band. IEEE 802.11g provides a data rate of 54 Mbps using orthogonal frequency division multiplexing (OFDM) in a 2.4 GHz band. IEEE 802.11n provides a data rate of 300 Mbps for four spatial streams using multiple input multiple output-OFDM (MIMO-OFDM). IEEE 802.11n supports a channel bandwidth of up to 40 MHz, and provides a data rate of 600 Mbps in this case.
With the fast popularization of such a WLAN and the diversification of applications using the WLAN, the necessity for new WLAN technology for supporting throughput higher than a data processing speed supported by IEEE 802.11n has increased. Very High Throughput (VHT) WLAN technology is one of IEEE 802.11 WLAN technologies proposed to support a data processing speed of a 1 Gbps or higher. Among the technologies, IEEE 802.11ac is a standard for providing very high throughput in a band of 6 GHz or less, and IEEE 802.11ad is a standard for providing very high throughput in a 60 GHz band.
In addition, standards for various WLAN technologies have been established, and the development of standards has been conducted. Representatively, IEEE 802.11af is a standard defined for the operation of a WLAN in TV white space, IEEE 802.11ah is a standard defined to support a large number of terminals operating in low power, and IEEE 802.11ai is a standard defined for fast initial link setup (FILS) in a WLAN system. Recently, in a congested environment in which multiple base stations and terminals are present, the development of an IEEE 802.11 high efficiency WLAN (HEW) standard aimed at improving frequency efficiency is ongoing.
In systems based on such WLAN technology, multiple terminals in a hidden node relationship may be present. In this case, a signal collision between terminals and retransmission caused by the signal collision frequently occur, thus resulting in a problem in which the efficiency of wireless channels is rapidly deteriorated.